The invention relates to improved radiation curable resin formulations and to methods for attaching a semiconductor chip to a nozzle plate for an ink jet pen using the improved radiation curable resin formulation.
Ink jet printers continue to evolve as the technology for ink jet printing continues to improve to provide higher speed, higher quality printers. The improvement in speed and quality does not come without a price, however. The ink jet pens of such printers are more costly to manufacture because of tighter alignment tolerances which must be met for the operative parts of the printers. One area of increased criticality is the alignment tolerance between the nozzle plate and semiconductor chip components of the ink jet pen.
During the manufacture of an ink jet pen for a thermal ink jet printhead, nozzle plates are aligned with semiconductor chips on the wafer so that heater resistors on the semiconductor chip used for heating the ink align with nozzle holes on the nozzle plate. Misalignment between the heater resistors and the nozzle holes has a disadvantageous effect on the accuracy of ink droplet placement of ink ejected from the nozzle holes to the print media. Heater resistor and nozzle plate alignment also has an effect on the mass and velocity of the ink droplet ejected through the nozzle hole.
There are multiple manufacturing steps required to produce an ink jet pen. First resistive, conductive and insulative metal layers are deposited on a silicon wafer to define individual semiconductor chips. Some of the layers, such as the resistive layers are disposed on discrete locations on each chip. Accordingly, the surface of the chips, on a microscopic scale, is substantially irregular or non-planar. The irregularities on the chip surface may cause poor adhesion between the nozzle plate and chip, misalignment of the nozzle holes in the nozzle plate with respect to the ink activators on the semiconductor chip, or in the worst case, delamination between the nozzle plate and chip.
Once the conductive, resistive and insulative layers are deposited on the wafer, and individual chips are defined, individual nozzle plates are attached to the chips after aligning the nozzle plates and chips to one another. The nozzle plate/chip assembly is then excised from the wafer and a TAB circuit or flexible circuit is then electrically connected to each of the semiconductor chips using a wire bonding or TAB bonding process. The resulting nozzle/plate chip and circuit assemblies are then each attached to a cartridge body in a chip pocket thereon using a die bond adhesive. Finally the TAB circuit or flexible circuit portion of the assembly is adhesively attached to the cartridge body. Because of the multiple adhesives used for making the ink jet pen, there are typically several curing steps required during the assembly of the pen components. With each assembly and curing step there is an opportunity for component misalignment to occur. Furthermore, handling of the pen during the assembly steps may cause delamination between the nozzle plates and chips.
Despite advances made in the art manufacturing ink jet pens for ink jet printers, there remains a need for improved formulations and methods for attaching nozzle plates to semiconductor chips for ink jet pens.
With regard to the foregoing and other objects, the invention provides a radiation curable resin formulation suitable for planarizing an ink jet heater chip. The resin formulation includes a multifunctional epoxy component, a difunctional epoxy component having a weight average molecular weight above about 2500, a silane coupling agent, an aryl sulfonium salt photoinitiator, and a non-photoreactive solvent. The resin formulation is substantially devoid of acrylate polymer components and the resin formulation contains from about 60 to about 85 weight percent of the difunctional epoxy component and from about 12 to about 22 weight percent of the photoinitiator based on the weight of the cured resin.
In another aspect the invention provides a method for making an ink jet pen for an ink jet printer. According to the method, a resin layer containing radiation curable resin formulation is applied to a surface of a semiconductor chip containing resistive and conductive layers on the surface thereof. The radiation curable resin formulation includes a multifunctional epoxy component, a difunctional epoxy component having a weight average molecular weight above about 2500, a silane coupling agent, an aryl sulfonium salt photoinitiator, and a non-photoreactive solvent. The resin formulation is substantially devoid of acrylate polymer components. After applying the resin layer to the surface, solvent is removed from the resin layer, and the resin layer is cured by exposure to actinic radiation to provide a cured resin layer. A nozzle plate is aligned and attached to the semiconductor chip with an adhesive to provide a nozzle plate/chip assembly. A TAB circuit or flexible circuit is attached to the nozzle pate/chip assembly. The cured resin layer contains from about 60 to about 85 weight percent of the difunctional epoxy component and from about 12 to about 22 weight percent of the photoinitiator.
In yet another aspect the invention provides a printhead for an ink jet printer. The printhead includes a cartridge body containing one or more pens attached thereto. Each pen includes a nozzle plate, a semiconductor chip having a device surface attached to the nozzle plate, a flexible circuit or TAB circuit attached to the semiconductor chip and a radiation cured resin layer applied to the device surface of the semiconductor chip in order to planarize the surface of the chip. The radiation cured resin layer is derived from a radiation curable resin formulation containing a multifunctional epoxy component, a difunctional epoxy component having a weight average molecular weight above about 2500, a silane coupling agent, a non-photoreactive solvent, and an aryl sulfonium salt photoinitiator. The resin formulation is substantially devoid of acrylate polymer components and the cured resin layer contains from about 60 to about 85 weight percent of the difunctional epoxy component and from about 12 to about 22 weight percent of the photoinitiator.
An advantage of the compositions and methods according to the invention is an improved adhesion between the nozzle plate adhesive and the radiation curable resin layer thereby reducing the incidence of delamination that may occur. The radiation curable resin layer also passivates the resistive and conductive metal layers on the chip and protects the layers from corrosion caused by components in the ink jet ink formulations. Enhanced protection of the circuitry from handling damage and debris is also provided by the radiation curable resin layer according to the invention. Other advantages of the radiation curable resin layer are that there is a substantial reduction in pigment flocculation on the surface of resin layer and the shelf life is believed to be substantially greater than with formulations containing acrylate polymer components such as polymethyl methacrylate resin.
For purposes of the invention, xe2x80x9cdifunctional epoxy materialsxe2x80x9d means materials having only two epoxy functional groups in the compound. xe2x80x9cMultifunctional epoxy materialsxe2x80x9d means epoxy materials having more than two epoxy functional groups in the compound.